Rotor blade with improved attachment on a hub of a fan

ABSTRACT

A rotor blade attached on a hub of a fan includes a blade-part, produced essentially of a composite material of fiber reinforced plastic, and an integrated foot having at least one body for attachment of the rotor blade on the hub of the fan, and at least one reinforcement which is essentially rigid in its longitudinal direction. The reinforcement is fastened to the body and extends at least along one of the sides of the blade. The body is arranged to withstand a state of strain, acting in several axially different directions. The body also extends perpendicular to the sides of the blade, and through the foot to both sides of the blade-part, so as to form a counterweight against a tendency of the blade to turn during operation.

TECHNICAL FIELD

The present invention relates to a rotor blade to be attached on a hubof a fan or the like, comprising a blade-part, produced essentially of acomposite material of fibre reinforced plastic, and an integrated foot,having at least one body for attachment of the rotor blade on the hub ofthe fan, and at least one reinforcement means which is essentially rigidin its longitudinal direction the reinforcement means, being fastened tothe body and extending at least along one of the sides of theblade-part.

BACKGROUND OF THE INVENTION

There is today a need of producing rotor blades of a material, which mayresist an aggressive environment, for instance, in the chemical processindustry, and which are relatively light, resulting in that the fan, onwhich the rotor blades are mounted, may be operated at higher speed andthat in certain cases, the rotor blades may also be made smaller andthus less expensive. Attempts have therefore been made to produce rotorblades of composite material, such as fibre reinforced plastic.

Through U.S. Pat. No. 4,877,376 a rotor blade of fibre reinforcedplastic is previously known, which has relatively low weight and mayaccordingly be operated at high speed. However, the fastening of therotor blade is complicated, partly due to a bolt joint having boltsextending through a pressure flange, abutting against the plasticmaterial, to a hub or an attachment device, and partly due to a shank,which extends into the attachment device and co-operates with means toprovide a pre-stress of the rotor blade. In an aggressive environmentsuch fastening is unsatisfactory, even if the material in the rotorblade is chemically resistant, the area around the pressure flange willbe both chemically and mechanically affected. Thus, it has been shownthat rotor blades, having fastening means of this kind, are subjected togreat stress, during high speed, and thus tend to be destroyed bypropagating cracks, arising in the area of the bolt joint.

Through U.S. Pat. No. 4,966,527 a rotor blade of fibre reinforcedplastic is also previously known, which has relatively low weight andmay accordingly be operated at high speed. However, the fastening of therotor blade is complicated, with fibres forming loops around severalmounting elements near the blade root, which elements extendsubstantially parallel to the sides of the blade.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a simple and durablefastening of a rotor blade made of composite material, which alsoresists an aggressive environment. An additional object is to improvethe operation conditions of the rotor blade.

These objects are achieved according to the invention with a rotorblade, which is characterised in that said body is arranged to withstanda state of strain, acting in several axially different directions, andthat said body extends, mainly perpendicular to the sides of the blade,through the foot to both sides of the blade-part, and comprisingfastening means located on each side of the blade-part.

In a preferred embodiment, the foot of the rotor blade comprises atleast two bodies, preferably made of metal, such as steel or similar,which effectively may withstand a state of strain, acting in severalaxially different directions. The two bodies extend perpendicularthrough the foot to both sides of the blade and suitably each bodyconsists of a beam, having a rounded lower edge. The two bodies may alsobe integrated with each other so as to from an H-shaped girderconstruction. Naturally, it is possible to use a body shaped like aplate, provided with recesses for the reinforcement means, or use onlyone beam, which by way of example is arranged obliquely in relation tothe blade.

The reinforcement means suitably comprise an amount of orientated fibresand includes in a preferred embodiment, at least a bundle carbon fibre,which during manufacturing of each rotor blade in a mould, is placedaround the body and lead out over the sides of the blade. Naturally, thereinforcement means may also be fastened to the body, for instance, byleading a bundle carbon fibre through a hole in the body, whereas it isfastened with a knot or similar, fastening having a larger diameter thanthe hole.

The composition of fibres and plastic in the composite material of thefoot of the rotor blade is preferably selected such that the compositematerial has an elongation by temperature adapted to the body. Thecomposite material is suitable made of glass-fibre reinforced epoxyresin.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described closer with reference to theattached drawings, in which;

FIG. 1 shows a partially cross-section, front view of a rotor bladeaccording to the present invention,

FIG. 2 shows a view from above of the rotor blade,

FIG. 3 shows a side-view of the rotor blade, and

FIG. 4 shows a cross-section of an area around the foot of the rotorblade, in larger scale.

DETAILED DESCRIPTION OF THE INVENTION

The drawings illustrate a rotor blade 1 for attachment on a hub of a fan(not shown) or the like. The rotor blade 1 comprises a blade-part 2 andan integrated foot 3. The foot 3 of the rotor blade comprise two bodies4, with fastening means 5. The two bodies 4 are preferably made ofmetal, such as steel or the like, which may withstand a state of strain,acting in several axially different directions. The two bodies 4 extendperpendicular in relation to the sides 7 of the blade, and through thefoot 3 to both sides of the blade-part 2. An amount of reinforcementmeans 6 extends at least partly around the two bodies 4 and along thesides 7 of the blade. The fastening means 5 may suitably include holesthrough the two bodies 4, which are intended to co-operate with bolts(not shown) screwed into the hub of a fan or into an attaching meansarranged thereto.

The rotor blade 1 is made of a composite material of fibre reinforcedplastic. In a preferred embodiment the composite material is areinforced glass-fibre in a matrix of epoxy resin, which according tothe invention are reinforced with an amount of reinforcement means 6 ofseveral equally orientated fibres. Preferably, the fibres are long andcontinuous, and may as an example be composed of carbon fibre, but alsoother fibres, for instance, fibres of aramide or similar may be used asreinforcement means. In the same way, polymer other than an then epoxyresin may be used as the matrix.

During production of the rotor blade 1 several layers of orientatedglass-fibres are placed on each side of a mould, then the bodies 4 arearranged in one end of the mould, a bundle of reinforcement means 6,such as carbon fibre, for example, being placed around each body 4 andbeing lead along a plastic core 8 (FIG. 4), which is arranged betweenthe layers of glass-fibre. Finally epoxy resin will be added.

Thus, the completed rotor blade 1 comprises a blade-part 2, made of acomposite material, and more particulary, a glass-fibre reinforced epoxyresin, provided with a core 8 of plastic and an integrated foot 3, whichlikewise is made of composite material and at least one body 4, andseveral reinforcement means 6 of carbon fibre.

Thus, the foot 3 of the rotor blade includes the body 4, thereinforcement means 6 and the part of the composite material locatedaround the body 4. Said body 4 extends, mainly perpendicular to thesides 7 of the blade, and through the foot 3, to both sides of theblade-part 2. By this, construction the body 4 forms a counterweightacting against the tendency of the blade-part 2 to turn around its ownaxle during operation. The body 4 is preferably made of metal, such assteel or similar, which may withstand a state of strain, acting inseveral axially different directions and has fastening means 5 on eachside of the blade-part 2, which, in the example shown, are shaped asbolt-holes for fastening a bolt. The number of bolt-holes may vary fromone to several bolt-holes on each side of the blade-part 2. As saidabove, the rotor blade 1 is fastened to a hub by means of the fasteningbolts, which are inserted in the holes of the body 4 and screwed intothe hub or into an attachment means arranged thereto. Even if thecomposite material essentially surrounds the body 4, it is advantageousthat the fastening bolts solely extend through the body 4 and that inthe area of the bolts there does not exist any essential amount ofcomposite material.

The rotor blade 1, described above, is light compared to earlier usedrotor blades made of metal, and it has proved to withstand high speedwithout bursting of the foot at the area of the bolt-joint. The forcesacting on the rotor blade 1 are transmitted via the reinforcement means6, such as carbon fibre, which is essentially stiff in its longitudinaldirection, to the body 4, which may withstand a state of strain, actingin several axially different directions, and further, via the fasteningbolts to the hub. An important part of the invention is that thereinforcement means 6 is fastened to the body 4, either by extendingaround the body 4 or being attached to the body 4 in a suitable manner.It is also important that the reinforcement means 6 extends over a partof the length of the rotor blades.

To avoid undesired stress of the reinforcement means, the body 4 isshaped as a beam, having rounded lower edges 4 a. It is possible to useonly one beam, even if the figures show use of two beams. It is alsopossible that the two bodies are integrated with each other and thusform an H-shaped girder construction 4 b or that the body is shaped likea plate, provided with recesses for fastening of the reinforcementmeans.

The composition of fibres and plastic in the composite material of thefoot 3 of the rotor blades is selected such that the composite materialhas an elongation dependent of the temperature, which is adapted to thebody 4, in such way that the effect of the bodies expansion duringdifferent temperature conditions will be reduced as much as possible,i.e. the composite material will follow the body 4 in its movementdependent of the temperature.

What is claimed is:
 1. Rotor blade to be attached on a hub of a fancomprising: a blade-part produced essentially of a composite material offibre reinforced plastic, and an integrated foot having at least onebody for attachment of the rotor blade on the hub of the fan and atleast one reinforcement means which is essentially rigid in itslongitudinal direction, said at least one reinforcement means beingfastened to the body and extending at least along one of the sides ofthe blade, wherein said at least one body is arranged to withstand astate of strain acting in several axially different directions, whereinsaid at least one body extends perpendicular to the sides of the bladeand through the foot to both sides of the blade-part so as to form acounterweight against a tendency of the blade to turn during operation,and wherein said at least one body includes fastening means located oneach side of the blade-part.
 2. Rotor blade according to claim 1,wherein a composite material essentially surrounds the at least onebody.
 3. Rotor blade according to claim 1, wherein the reinforcementmeans includes a number of equally orientated fibres.
 4. Rotor bladeaccording to claim 3, wherein the reinforcement means extends at leastpartly around the at least one body.
 5. Rotor blade according to claim3, wherein the reinforcement means is attached to the at least one body.6. Rotor blade according Lo claim 1, wherein said at least one bodycomprises two beam-shaped bodies which are designed with a rounded loweredge.
 7. Rotor blade according to claim 6, wherein the two bodies areintegrated with each other so as to form an H-shaped girderconstruction.
 8. Rotor blade according to claim 1, wherein the at leastone body is shaped like a plate, provided with recesses for fastening ofthe reinforcement means.
 9. Rotor blade according to claim 1, whereinthe composite material includes a glass-fibre reinforced epoxy resin,and the reinforcement means include carbon fibre.
 10. Rotor bladeaccording to claim 1, wherein the at least one body is made of metal.11. Rotor blade according to claim 2, wherein the reinforcement meansincludes a number of equally oriented fibres.
 12. Rotor blade accordingto claim 11, wherein the reinforcement means extends at least partlyaround the at least one body.
 13. Rotor blade according to claim 11,wherein the reinforcement means are attached to the at least one body.14. Rotor blade according to claim 2, wherein said at least one bodycomprises two beam-shaped bodies which are designed with a rounded loweredge.
 15. Rotor blade according to claim 3, wherein said at least onebody comprises two beam-shaped bodies which are designed with a roundedlower edge.
 16. Rotor blade according to claim 2, wherein the at leastone body is shaped like a plate, provided with recesses for fastening ofthe reinforcement means.
 17. Rotor blade according to claim 3, whereinthe at least one body is shaped like a plate, provided with recesses forfastening of the reinforcement means.
 18. Rotor blade according to claim2, wherein the composite material includes a glass-fibre reinforcedepoxy resin, and the reinforcement means include carbon fibre.
 19. Rotorblade according to claim 3, wherein the composite material includes aglass-fibre reinforced epoxy resin, and the reinforcement means includecarbon fibre.
 20. Rotor blade according to claim 2, wherein the at leastone body is made of metal.